Both the game and the TV drama are set in 2046, some 30 years after the Votan collective of alien species arrived in the skies over Earth. After a brutal war, the humans and aliens have settled into an uneasy peace, but alien technology that crashed to Earth has drastically changed the landscape.

The “Defiance” game shows the effects of these “arkfalls” on California’s Bay Area, now a wasteland packed with bloodthirsty mutants, hostile cyborgs and overgrown, fire-spewing insects. Your character – male or female, human or Votan – is an ark hunter who makes a living by scavenging from crash sites, and the search for a particular alien artifact brings you to the West Coast.

Soon after your arrival, the game’s sprawling map opens up, letting you choose from dozens of missions. You can race dune buggies around the wilderness. You can infiltrate raider strongholds and steal their loot. You can rescue farmers from “hellbug” infestations. Most missions can be handled solo, but if you stumble across a major arkfall you’re going to need help from other online players.

You’ll also discover “episode missions” that relate to the next week’s installment of the “Defiance” TV show. In the first such adventure, you meet military veteran Joshua Nolan and his partner, an alien named Irisa.

The titular town of Defiance was built on the ruins of St. Louis, so I don’t know how many of its characters will visit us ark hunters out West. But both sides of the “Defiance” team have collaborated on building an impressive world, and I’m eager to see where they go from week to week.

I was able to battle through the initial batch of episode missions in just a few hours, but there’s plenty more to do. As with any online shooter, you can engage in raucous death matches with your fellow humans. Or you can enroll in the Shadow War, in which huge teams of up to 64 players each battle for control of sites all over the map.

Such massively multiplayer epics are popular among computer gamers, but we haven’t seen many on consoles. I’ve been playing “Defiance” on the Xbox 360, and I love being able to use an Xbox controller instead of a PC’s keyboard and mouse. On the other hand, I was frequently unable to log onto Trion’s servers during the first few days after the game went on sale. That problem has eased up, but there are still too many glitches, from unresponsive controls to disappearing inventory items.

There’s also a wearying sameness to the bulk of the missions, which typically consist of racing to a location, killing a bunch of monsters and retrieving some object. The action is intense and challenging, often reminiscent of 2K Games’ fine “Borderlands.” But it’s missing that series’ twisted sense of humor, and I’m hoping Trion delivers more variety in future episodes.